public static void Day21_1_2(IReadOnlyList <string> input)
{
var registers = new int[REGISTERS];
var ipRegister = Day19.GetIpRegister(input);
var instructions = Day19.GetInstructions(input);
var operators = Day19.GetOperators();
var set = new HashSet <int>();
int lastNewSeen = 0;
while (registers[ipRegister] < instructions.Length)
{
var instruction = instructions[registers[ipRegister]];
registers = operators[instruction[0]](registers, instruction);
if (registers[ipRegister] == 28 &&
!set.Contains(registers[3]))
{
lastNewSeen = registers[3];
if (!set.Any())
{
Console.WriteLine($"Part 1: {lastNewSeen}");
}
set.Add(lastNewSeen);
}
else if (registers[ipRegister] == 28)
{
Console.WriteLine($"Part 2: {lastNewSeen}");
break;
}
registers[ipRegister]++;
}
}